The present invention relates to a ratchet mechanism and more particularly to a ratchet mechanism which, when operative, permits a rotatable member to rotate freely in one direction whilst locking the rotatable member against rotation in the opposite direction.
Pulley blocks are widely used and commonly comprise a pulley wheel or sheave mounted by way of ball bearings between two block cheeks. It has been proposed to provide such a pulley block with a ratchet. In a typical pulley block of this type a sheave has a toothed inner periphery and the ratchet mechanism includes an engaging member suitable for engaging this toothed inner periphery. Some form of switch is usually provided to move the engaging member between an engaged position and a disengaged position. The switch usually projects through an aperture in the block cheek and may be operated manually.
Such a pulley block incorporating a ratchet mechanism may be used to facilitate raising or moving heavy objects or resistive loads where it is obviously undesirable for the object being moved to slip back in the opposite direction to the desired direction of movement. Such blocks are used on yachts to raise and lower the sails. Thus, it will be appreciated that it is highly undesirable for the member which engages the toothed inner periphery of the sheave to accidentally become disengaged from the toothed inner periphery during operation.